1. Field of the Invention
The present invention generally relates to patterning of microelectronic devices, and more particularly to CMP assisted liftoff micropatterning of vacuum deposited thin films for microelectronic devices and nanostructures.
2. Description of the Related Art
Patterning materials using photoresists and etching is a technology known in the art, which has been advanced by progress in microelectronics where structures on the order of 100 nm are used, particularly for very large scale integrated (VLSI) silicon chips and for magnetic recording heads for computer disk drives. Some vacuum deposited thin film materials are not easily etched. U.S. Pat. No. 3,873,361 issued to Franco et al. teaches that such materials can be patterned by depositing them through a stencil of photoresist with an overhanging cross-section. The material within the stencil remains after the photoresist is stripped off in a solvent, removing it and the overlying film. This lift-off process has been used in silicon microcircuits and particularly in thin-film recording heads, particularly for defining the magnetoresistive read sensor and its conductive leads. Creating patterns with gaps smaller than a few hundred nanometers has become exceeding difficult because the depth of the overhanging structure is limited, and material deposited on the resist forms very undesirable sharp fences when the resist is lifted off. U.S. Pat. No. 5,246,884 issued to Jaso et al. teaches that thin polish resistant layers such as diamond-like carbon (DLC) can be used as a gauge layer to stop chemical-mechanical polishing (CMP).
In a liftoff process for attaching electrical leads to a magnetically sensitive resistor (giant magnetoresistive or GMR sensor), one starts with a sensor film which has its dimensions between the leads defined by an ion mill (argon sputter etch) process which removes the GMR sensor within the overhanging photoresist opening where the sensor will be deposited. Then, when the sensor is deposited, using the same photoresist pattern, the deposited film will be aligned (self-aligned) with the conductive leads deposited into the same photoresist structure.
In the self-aligned process, the ion mill process uses a bi-layer resist where the effective photoresist mask is raised off the wafer in order to achieve the necessary undercut, wherein the edge of the sensor has a relatively small angle. Similarly, when the leads are deposited, they taper as they cover this shallow angle of deposition. This makes the exact length of the GMR sensor difficult to determine and control.
The major problems with the related art are several. First, the liftoff process does not scale for sub-micron sized structures of perhaps 250 nanometers because the undercut becomes too small. Second, for the example of very small magnetic read sensors, it is desirable to have the ion mill process give steep (nearly vertical) sidewalls so that the read sensor resistors and their self-aligned electrical leads could be well defined. Such geometry has not been produced by the conventional processes. Finally, the thin polish resistant layers do not clearly protect both the deposited film and the previous surface features in the conventional processes. In fact, it is focused on achieving some degree of planarity. Therefore, there is a need for a new micropatterning technique capable of scaling to sub-micron sized devices for materials that are difficult to etch.